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Controversial insecticides known as neonicotinoids pose a danger to wild bees and managed honey bees, the European Food Safety Authority (EFSA) in Parma, Italy, said in a report released today. Bayer, a maker of so-called neonics, disputed EFSA's findings. But the report is likely to give a boost to those pushing for tighter European regulation of the chemicals.

“This report certainly strengthens the case for further restrictions on neonicotinoid use,” entomologist Dave Goulson of the University of Sussex in Brighton, U.K., said in a statement. The European Commission last year proposed—but has not yet adopted—extending a partial ban on neonics to all field crops.

Neonicotinoids are systemic pesticides. Often, they are used to coat seeds to protect them when they are planted in the ground. After the seed germinates, the pesticide spreads throughout the growing plant and guards it against nibbling insects. But the insecticide is also present in the nectar and pollen, meaning pollinators get dosed, too. Many studies have shown that the chemicals can affect the ability of honey bees to learn and forage, although industry scientists have disputed whether the experiments are realistic enough.

In 2013, the commission banned the use of three neonics—imidacloprid, clothianidin, and thiamethoxam—on flowering field crops such as corn, sunflower, and rapeseed. The pesticides can still be used in greenhouses, winter cereals, and for spraying certain crops after they flower. The ban was based on a review by EFSA.

Starting in 2015, EFSA staff analyzed 588 new studies, including some that looked at effects on bumble bees and solitary bees. The conclusion: Most uses of neonics pose a risk to both managed honey bees and wild bees, although the level of risk varies by species and route of exposure. The three pesticides can hinder learning and navigation in bees, for example, and harm reproduction. One likely way that wild bees are exposed is through contamination of plants other than the crops. Neonicotinoids in farm soil can spread via water or wind-blown dust to nearby ground, where the pesticides are absorbed by weeds and wildflowers. EFSA admitted that “information on this phenomenon is somewhat limited” but concluded that it could be a way for bees to be exposed to harmful amounts of neonics.

Christopher Connolly of the University of Dundee School of Medicine in the United Kingdom noted in a statement that chronic presence of neonics in the environment will “inevitably” help pests evolve resistance. “A highly restricted use of neonicotinoids would reduce this environmental stress and retain neonicotinoids as important pest control agents for use in severe situations.”

Bayer, a major manufacturer of neonics, “fundamentally disagrees” with the EFSA conclusion, saying that U.S. and Canadian regulators have determined that neonicotinoids are safe for honey bees.

The commission, however, endorsed EFSA's report. “This is strengthening the scientific basis for the Commission's proposal to ban outdoor use of the three neonicotinoids,” according to a commission statement.

Last year, the commission proposed extending the neonic ban to all field crops, allowing an exemption for greenhouses. It hoped for a vote in early 2018. Support was mixed: This past December, 11 EU nations endorsed the wider ban, whereas six opposed it and 11 took no stance. Many wanted to wait until EFSA chimed in. On 22 March, the commission's Standing Committee on Plants, Animals, Food and Feed is set to discuss the new EFSA report. No date has been scheduled for a vote on the commission's proposed expansion of the ban.